Wireless access systems have been widely deployed to provide various types of communication services such as voice or data. In general, a wireless access system is a multiple access system that supports communication of multiple users by sharing available system resources (a bandwidth, transmission power, etc.) among them. For example, multiple access systems include a Code Division Multiple Access (CDMA) system, a Frequency Division Multiple Access (FDMA) system, a Time Division Multiple Access (TDMA) system, an Orthogonal Frequency Division Multiple Access (OFDMA) system, and a Single Carrier Frequency Division Multiple Access (SC-FDMA) system.
Recently, the structure of a radio access system has changed to a structure in which small cells (e.g., pico cells, femto cells, etc.) having various shapes and small sizes are connected to a macro cell having a relatively large size. This aims to enable a user equipment (UE), which is an end user, to receive a high data rate to increase quality of experience in a state in which multilayered cells having vertical layers, in which conventional macro cells are fundamentally involved, are mixed.
However, in an environment in which a large number of small cells is arranged, a UE may be connected to two or more small cells to transmit and receive data. At this time, the UE shall transmit control information of several small cells using a restricted uplink control channel. Accordingly, there is a need to transmit uplink control information using a method different from that of a legacy cellular system.